The present invention relates to magnetic field sensors, and more particularly relates to a thin film magnetic sensor formed using a self-organizing polymer mask to create a patterned magnetic thin film.
The magnetoresistance effect has been exploited for use in electronic sensors and equipment, such as in the read/write head of magnetic storage systems. The giant magnetoresistance effect (GMR) is said to be present when a sensor exhibits a change in resistance (xcex94R/R) between a magnetically random state and a magnetically saturated state exceeds about 0.5%.
In order to take advantage of the giant magnetoresistance (GMR) effect in the read head of a magnetic storage system, the device must respond to magnetic fields of the order of 100 Oe. The giant magnetoresistance effect has been observed in multilayer devices such as for example, in a publication by S. Parkin et al., Phys. Rev. Lett. 64, 2304 (1990). The giant magnetoresistance effect has also been observed in phase separated, granular Cuxe2x80x94Co films, such as exemplified in a publication by J. Q. Xiao et al., Phys. Rev. Lett. 68, 3749 (1992). In the case of granular films, a polycrystalline metastable Cuxe2x80x94Co alloy film is deposited. With appropriate heat treatment, Co precipitates as single domain particles. Absent the presence of magnetic fields, the magnetization is oriented along the easy axes of each particle, which varies randomly from particle to particle. Thus, in a zero applied magnetic field, the resistance is high because the electrons scatter at each interface where the magnetic orientation changes. At magnetic saturation, the resistance is low to electrons because the magnetization of all of the particles is aligned. However, to reach saturation, the magnetic field must overcome the magnetocrystalline anisotropy and the shape anisotropy of the Co particles. In addition, if there is any interfacial strain at the Cu/Co interface, there may be an additional anisotropy through the magnetostriction (xcex). These factors reduce the sensitivity of the sensor.
U.S. Pat. No. 5,565,236 to Gambino et al. discusses the fabrication of a GMR sensor which includes a granular layer of magnetic particles suspended within a copper matrix. The ""236 patent teaches that the granular layer should be textured in order to align the magnetic particles such that there easy axis is aligned along the plane of the layer, which provides a more sensitive magnetic sensor. The process of manufacturing the sensor uses precipitation to generate the sub-micron magnetic particles. While the sensor of the ""236 patent provides high sensitivity, it would be desirable to provide a simpler method of manufacturing a highly sensitive monolithic magnetic field sensor.
It is an object of the present invention to provide an improved method of manufacturing a magnetic field sensor.
In accordance with the present invention, a method of forming a magnetic field sensor on a substrate includes the steps of forming a layer of magnetic material supported by the substrate, coating the magnetic material with a diblock copolymer film, and self organizing the copolymer film into mesa regions of a first monomer and valley regions of a second monomer. Next, an etching step is used to remove the second monomer from the valley portions and underlying magnetic material while only partially etching the first monomer, thereby forming a patterned magnetic thin film of magnetic islands corresponding to the mesa regions. The magnetic islands are interconnected with a non-magnetic conductive layer and electrical contacts are connected thereto.
Also in accordance with the present invention, a magnetic field sensor includes a substrate and a patterned magnetic thin film having a plurality of magnetic island regions supported by said substrate. The sensor further includes a non-magnetic conductive layer electrically interconnecting the magnetic island regions. First and second electrical contacts are operatively coupled to the conductive layer at first and second locations, respectively, to facilitate connection of the magnetic field sensor to outside devices, circuits, etc.
These and other features, objects and advantages of the present invention will be apparent from reading the following detailed description of preferred embodiments together with the accompanying drawings, and the scope of the invention will be set forth in the appended claims.